title: Properties of single fibers in global extraocular muscle of the cane toad, Bufo marinus

authors: Halsey, Elizabeth Hope

abstract: Very limited information exists on the contractile physiology of the specialized muscle fibers that make up vertebrate extraocular muscle (EOM). This study was undertaken to measure some contractile properties of fibers in the global region of EOM using the cane toad, Bufo marinus, and in particular the tonic or multiply-innervated fibers (MIFs). Fiber types were characterized using a number of methods.

Tonic and twitch fibers were identified in EOM using transmission electron microscopy. Tonic fibers lacked an M-line, had sparse sarcoplasmic reticulum (SR), few mitochondria and a thick Z-line. Some twitch fibers showed the presence of lipid stores and abundant mitochondria, whereas others were distinguished more by well developed SR. In transverse section, tonic fibers showed a felderstruktur pattern of fused myofibrils and the twitch fibers displayed a fibrillenstruktur pattern of well-delineated myofibrils.

The distribution and diameter of tonic and twitch fibers in the global region were characterized using histochemistry. Transverse sections stained for mATPase, α-GPDH and NADH-TR activity revealed the presence of at least three different fiber types in global EOM of Bufo marinus. Tonic fibers showed little or no activity for all three enzymes and were distributed randomly within the global region where they made up about 20% of the fibers. Tonic fibers always occurred at lower frequencies than twitch fibers at all diameter ranges analysed. Two further types of fiber were characterized by their histochemical appearance as twitch light and twitch dark.

Force-pCa relationships were determined for chemically skinned single fibers by recording peak isometric force at maximal and submaximal calcium activation. Fibers were found to differ in their force response to initial and maximal calcium activation. Force-pCa data were fitted to Hill plots and Hill coefficients, n₁ and n₂, obtained for responses at high and low calcium concentrations, respectively. This information together with diameter and appearance (clear versus dark) also allowed fibers to be divided into three groups. Tonic fibers developed tension slowly and had significantly lower maximum normalized tension and n₂ values than twitch light fibers. Twitch dark and twitch light fibers developed tension rapidly in response to initial and maximal calcium activation and had similar n₂ values. However, twitch dark fibers had a significantly lower maximum normalized tension than twitch light fibers. The pCa₅₀ values did not differ between the three groups of fibers. Fiber classifications were corroborated by single fiber transmission electron microscopy (TEM). SDS-PAGE followed by silver staining was used to resolve the MLC components of single fibers for which force-pCa relationships were known. Both twitch light and twitch dark fibers had three myosin light chains, each having the same electrophoretic mobility as the light chains from the fast-twitch rabbit psoas muscle. The tonic fibers were found to lack the low molecular weight light chain, myosin light chain three (MLC3), and the regulatory light chain (MLC2) of these fibers showed reduced mobility compared to that of the twitch fibers.

The finding that tonic fibers responded in a different manner to initial and maximal calcium activation from twitch fibers can be used by others to aid in their identification. The significantly different responses of twitch and tonic fibers to maximal and submaximal calcium activation highlight the extent to which these fiber types differ. Additional work using single fibers will undoubtedly reveal further differences in the composition and functioning of contractile proteins in EOM fibers.

text: Properties of single fibers in global extraocular muscle of the cane toad, Bufo marinus Very limited information exists on the contractile physiology of the specialized muscle fibers that make up vertebrate extraocular muscle (EOM). This study was undertaken to measure some contractile properties of fibers in the global region of EOM using the cane toad, Bufo marinus, and in particular the tonic or multiply-innervated fibers (MIFs). Fiber types were characterized using a number of methods.

Tonic and twitch fibers were identified in EOM using transmission electron microscopy. Tonic fibers lacked an M-line, had sparse sarcoplasmic reticulum (SR), few mitochondria and a thick Z-line. Some twitch fibers showed the presence of lipid stores and abundant mitochondria, whereas others were distinguished more by well developed SR. In transverse section, tonic fibers showed a felderstruktur pattern of fused myofibrils and the twitch fibers displayed a fibrillenstruktur pattern of well-delineated myofibrils.

The distribution and diameter of tonic and twitch fibers in the global region were characterized using histochemistry. Transverse sections stained for mATPase, α-GPDH and NADH-TR activity revealed the presence of at least three different fiber types in global EOM of Bufo marinus. Tonic fibers showed little or no activity for all three enzymes and were distributed randomly within the global region where they made up about 20% of the fibers. Tonic fibers always occurred at lower frequencies than twitch fibers at all diameter ranges analysed. Two further types of fiber were characterized by their histochemical appearance as twitch light and twitch dark.

Force-pCa relationships were determined for chemically skinned single fibers by recording peak isometric force at maximal and submaximal calcium activation. Fibers were found to differ in their force response to initial and maximal calcium activation. Force-pCa data were fitted to Hill plots and Hill coefficients, n₁ and n₂, obtained for responses at high and low calcium concentrations, respectively. This information together with diameter and appearance (clear versus dark) also allowed fibers to be divided into three groups. Tonic fibers developed tension slowly and had significantly lower maximum normalized tension and n₂ values than twitch light fibers. Twitch dark and twitch light fibers developed tension rapidly in response to initial and maximal calcium activation and had similar n₂ values. However, twitch dark fibers had a significantly lower maximum normalized tension than twitch light fibers. The pCa₅₀ values did not differ between the three groups of fibers. Fiber classifications were corroborated by single fiber transmission electron microscopy (TEM). SDS-PAGE followed by silver staining was used to resolve the MLC components of single fibers for which force-pCa relationships were known. Both twitch light and twitch dark fibers had three myosin light chains, each having the same electrophoretic mobility as the light chains from the fast-twitch rabbit psoas muscle. The tonic fibers were found to lack the low molecular weight light chain, myosin light chain three (MLC3), and the regulatory light chain (MLC2) of these fibers showed reduced mobility compared to that of the twitch fibers.

The finding that tonic fibers responded in a different manner to initial and maximal calcium activation from twitch fibers can be used by others to aid in their identification. The significantly different responses of twitch and tonic fibers to maximal and submaximal calcium activation highlight the extent to which these fiber types differ. Additional work using single fibers will undoubtedly reveal further differences in the composition and functioning of contractile proteins in EOM fibers.

year: 1999

title: Bounded natural frequencies of completely free rectangular plates

authors: Mochida, Yusuke

abstract: This paper presents dimensionless natural frequency parameters for completely free rectangular plates, calculated using the superposition method (SM) and the finite difference method (FDM). The convergence tests show that while the SM gives upper bound results the FDM gives lower bound results. The results obtained using the FDM appears to be the best lower bound results available to date. Together with the upper bound results from the SM, the maximum possible error in the first 12 non-zero natural frequency parameters for completely free rectangular plates of various aspects ratios ranging from 1:1 to 3:1 can be determined from the results presented here.

text: Bounded natural frequencies of completely free rectangular plates This paper presents dimensionless natural frequency parameters for completely free rectangular plates, calculated using the superposition method (SM) and the finite difference method (FDM). The convergence tests show that while the SM gives upper bound results the FDM gives lower bound results. The results obtained using the FDM appears to be the best lower bound results available to date. Together with the upper bound results from the SM, the maximum possible error in the first 12 non-zero natural frequency parameters for completely free rectangular plates of various aspects ratios ranging from 1:1 to 3:1 can be determined from the results presented here.

year: 2008

title: The presence of the past: Maori history in contemporary reflection

authors: Mahuika, Nepia

abstract: This is the opening line of a famous saying in my tribe. For our people - Ngāti Porou - these words have become embedded in our tribal identity as important directives that we are encouraged to aspire to. In the “days destined to you”, Ngata reminds us that each generation has its own mana (or authority), our own responsibilities and challenges, our own dreams and destinies to fulfil, and our own histories to tell about Ngāti Porou: who we are, our past, present, and future. If we consider this expectant, and I think hopeful, affirmation as a gift and responsibility, then taking real ownership of the “days destined to us” requires us to know what our forebears have entrusted us with. What are those historical gifts that we might use to “centre” and assert ourselves as Māori, as Ngāti Porou? We might look at this directly, i mua: the past before us because it is our history that is so crucial to us as we walk consciously, and with determination, into the future. Our past before us helps us to know where we are going, it helps us correc our course when we stray, keeps us mindful of the “kaupapa”: whatever that might be in our generation and corner of the Maori universe. We’ve heard already today from both Enoka and Arini how Māori, in our own ways, are engaging with our past, drawing on our korero tuku iho (our oral histories passed down across the generations), on our whakairo (our carving), to illuminate the many ways Māori do, and think about, the past.

text: The presence of the past: Maori history in contemporary reflection This is the opening line of a famous saying in my tribe. For our people - Ngāti Porou - these words have become embedded in our tribal identity as important directives that we are encouraged to aspire to. In the “days destined to you”, Ngata reminds us that each generation has its own mana (or authority), our own responsibilities and challenges, our own dreams and destinies to fulfil, and our own histories to tell about Ngāti Porou: who we are, our past, present, and future. If we consider this expectant, and I think hopeful, affirmation as a gift and responsibility, then taking real ownership of the “days destined to us” requires us to know what our forebears have entrusted us with. What are those historical gifts that we might use to “centre” and assert ourselves as Māori, as Ngāti Porou? We might look at this directly, i mua: the past before us because it is our history that is so crucial to us as we walk consciously, and with determination, into the future. Our past before us helps us to know where we are going, it helps us correc our course when we stray, keeps us mindful of the “kaupapa”: whatever that might be in our generation and corner of the Maori universe. We’ve heard already today from both Enoka and Arini how Māori, in our own ways, are engaging with our past, drawing on our korero tuku iho (our oral histories passed down across the generations), on our whakairo (our carving), to illuminate the many ways Māori do, and think about, the past.

year: 2016