The steady-state force–Ca2+ relationship in intact lobster

dc.contributor.authorCavey, Michael J.en
dc.contributor.authorShinozaki, T.en
dc.contributor.authorWilkens, J. L.en
dc.contributor.authorYazawa, T.en
dc.contributor.authorter Keurs, H. E. D. J.en
dc.contributor.departmentBiological Sciencesen
dc.contributor.facultyFaculty of Scienceen
dc.contributor.institutionUniversity of Calgaryen
dc.date.accessioned2006-08-14T17:08:22Z
dc.date.available2006-08-14T17:08:22Z
dc.date.issued2004-05-07
dc.description.abstractThe heart of the decapod crustacean is activated by regular impulse bursts from the cardiac ganglion. The cardiac pump function depends on ganglionic burst frequency, burst duration, and burst impulse frequency. Here, we activated isolated lobster cardiac ostial muscle (Orbicularis ostii muscle, OOM) by stimulus trains in vitro in order to characterize the response of the contractile apparatus to [Ca2+]i . We employed stimulus trains that generate a steady state between the [Ca2+]i and force in order to estimate the Ca2+ sensitivity of myofilaments. Force and [Ca2+]i transients were simultaneously recorded using a silicon strain gauge and the fluorescence of iontophoretically microinjected fura-2 salt. We examined the effects of tetanus duration (TD), the interval between trains, and 6 lM cyclopiazonic acid, an inhibitor of the SR Ca2+ pump, on the steadystate force–[Ca2+]i relationship. The instantaneous force–[Ca2+]i relationships appeared sigmoidal (EC50 and Hill coefficient, 98.8±32.7 nM and 2.47±0.20, mean ± SD, respectively), as did the curves superimposed after 500 ms following the start of stimulation, indicating that the force–[Ca2+]i relationship had reached a steady state at that time. Also, the maximum activated force (Fmax) was estimated using the steadystate force–[Ca2+]i relationship. Prolonged stimulus trains, decreasing the interval between recurrent trains from 5 to 2.5 s, and cyclopiazonic acid each increased the measured EC50 without changing Fmax. The EC50 correlated strongly with averaged [Ca2+]i over time. We conclude that the steady-state force–[Ca2+]i relationships in the OOM indicate cooperation between force generation and Ca2+ binding by the myofilaments. Our data also suggest the existence of a novel Ca2+-dependent mechanism which reduces Ca2+ sensitivity and accelerates relaxation of lobster cardiac muscle myofilaments. http://www.springerlink.com/content/n343yxe5clj0b40n/?p=7981f8215b7a455f96538d280dbad79aπ=5en
dc.description.refereedyesen
dc.format.extent327852 bytes
dc.format.mimetypeapplication/pdf
dc.identifier.citationT. Shinozaki, J. L. Wilkens, T. Yazawa, M. J. Cavey, H. E. D. J. ter Keurs " The steady-state force–Ca2+ relationship in intact lobster ( Homarus americanus) cardiac muscle" J Comp Physiol B (2004) 174: 407–414 DOI 10.1007/s00360-004-0427-3en
dc.identifier.doihttp://dx.doi.org/10.11575/PRISM/35112
dc.identifier.issn0174-1578
dc.identifier.urihttp://hdl.handle.net/1880/43411
dc.language.isoenen
dc.publisherSpringer-Verlagen
dc.publisher.urlhttp://www.springerlink.com/content/1432-136X/
dc.subjectBiologyen
dc.subject.otherHomerus americanusen
dc.subject.otherOrbicularis ostii muscleen
dc.subject.otherForce–[Ca2+]i relationshipen
dc.subject.otherTrain intervalen
dc.subject.otherTetanus durationen
dc.titleThe steady-state force–Ca2+ relationship in intact lobsteren
dc.typejournal article
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