Abstract
Local calcium stimuli (artificial sparks) generated by 2-photon breakdown of the cage NDBF-EGTA were applied to evoke Ca release from the SR in single skeletal or cardiac muscle cells undergoing fast Ca imaging with the low affinity dye fluo 4FF. The figure shows selected sequential images of the Ca transient generated by a frog skeletal muscle fiber with permeabilized plasmalemma, in response to a spark (elicited outside the fiber to avoid photodamage). Two types of responses were observed: (i) an all-or-none wave -shown- that propagates over the entire cell and (ii) graded responses, which fail to propagate. Release analysis (Rios, JGP 1999; Figueroa, this meeting) separates SR release from simple diffusion of photo-released Ca into cells. The technique yields a sensitive measure of threshold [Ca2+] for release activation, which in the example (0.3 mM [Mg2+]cyto) was 1 μM, and can monitor inactivation by combining multiple stimuli. Modeling of these responses aims at describing quantitatively the properties of activation, as well as the roles of inactivation and depletion in the control of Ca release. Other details and acknowledgments are presented elsewhere (Figueroa, this meeting.)View Large Image | View Hi-Res Image | Download PowerPoint Slide
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