Transsarcolemmal calcium movements in arterially perfused rabbit right ventricle measured with extracellular calcium-sensitive dyes.
Activation-dependent changes of mean extracellular calcium concentrations were monitored spectrophotometrically in arterially perfused right ventricle of rabbit via extracellular application of the calcium-sensitive absorption dyes, antipyrylazo III and tetramethylmurexide. After rest periods of 3 minutes or longer, 10% of total dye-accessible calcium (300-500 microM) is depleted cumulatively from the extracellular space by four to eight beats at 2 Hz stimulation. During continued stimulation, or during quiescence following a depletion response, mean extracellular calcium concentrations return toward the prestimulatory level in the course of 2-4 minutes. A single stimulation placed 2-30 seconds subsequent to rapid pacing results in a potentiated beat with an accompanying net increment of mean extracellular calcium. Total dye-accessible calcium can increase by at least 4% at such a beat, and depletion responses can be repeated immediately thereafter. During a sequence of such responses, extracellular calcium lost cumulatively during three to five rapid beats is replenished, for the most part, by a single post-stimulatory beat. These results demonstrate that most of the "activator pool" of cellular calcium can turn over to the extracellular space during a single contraction cycle in rabbit myocardium, and suggest that, in mammalian myocardium, diastolic calcium efflux may be quantitatively negligible in relation to efflux during excitation-contraction coupling.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004396:Coloring Agents; D004558:Electric Stimulation; D007473:Ion Channels / Q000378:metabolism*; D008027:Light; D008297:Male; D009114:Murexide / Q000031:analogs & derivatives; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D009282:Naphthalenesulfonates; D010477:Perfusion; D011817:Rabbits; D012508:Sarcolemma / Q000378:metabolism*
D004396:Coloring Agents; D007473:Ion Channels; D009282:Naphthalenesulfonates; C026042:tetramethylmurexide; D009114:Murexide; C016238:antipyrylazo III; D002118:Calcium