Transsarcolemmal calcium movements in arterially perfused rabbit right ventricle measured with extracellular calcium-sensitive dyes.

Abstract

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.

Effect of Ion Concentration Changes in the Limited Extracellular Spaces on Sarcolemmal Ion Transport and Ca2+ Turnover in a Model of Human Ventricular Cardiomyocyte

“…In addition, our simulations show that, upon returning to 1 Hz, a transient accumulation of Ca 2+ took place in the cleft space with a very similar time course as the former depletion. This compares well with Ca 2+ depletion measured in the perfused right ventricular tissue of rabbits (amounting to 0.3 to 0.5 mM) reported by Hilgemann and Langer [22] in a train of eight stimulations at 0.5-s intervals applied from rest.…”

Extracellular calcium as an integrator of tissue function

“…In general, such methods require experiments to be performed in limited volumes and at low [Ca 2+ o ]. Impermeant Ca 2+ dyes were used to estimate Ca 2+ o decreases during a cardiac action potentials (Cleemann et al, 1984;Hilgemann & Langer, 1984;Hilgemann, 1986), allowing inferences about the magnitude and timing of Ca 2+ influx into cardiac myocytes in multicellular preparations. A further iteration in the development of a reliable means of measuring Ca 2+ o fluctuations with Ca 2+ -sensitive fluorophores is the droplet technique, developed by Drs.…”

“…Polarized expression and targeting of Ca 2+ permeable ion channels, the plasma membrane Ca 2+ ATPase (PMCA) and/or the Na + /Ca 2+ exchanger (NCX) can create distinct plasma membrane compartments specialized for Ca 2+ influx and efflux, potentially creating areas of extracellular accumulation or depletion of Ca 2+ , particularly coupled with restricted diffusion spaces within a tissue. The differential distribution of Na + , Ca 2+ and K + channels, and both PMCA and NCX between cardiac sarcolemmal and T tubular membranes produces the efficient release of intracellular Ca 2+ from the sarcoplasmic reticulum and rapid recovery of Ca 2+ i during diastole (Brette & Orchard, 2003), which is reflected in the reduction and recovery of [Ca 2+ ] in the T tubules during each contraction (Cleemann et al, 1984;Hilgemann & Langer, 1984;Hilgemann, 1986). Similarly, the global decreases in [Ca 2+ o ] observed in intact rat brain after hypoxia (Silver & Ercińska, 1990) can be attributed to the highly specialized expression and distribution of voltage-and neurotransmitter-activated Ca 2+ permeable channels at the preand postsynaptic membranes (Rusakov et al, 1999;Juhaszova et al, 2000, Wiest et al, 2000Stanley, 2000).…”

Extracellular calcium transients and action potential configuration changes related to post-stimulatory potentiation in rabbit atrium.

“…The apparent activation dependence of calcium efflux, suggested by these early considerations, has been a latent problem in the study of cardiac excitation-contraction coupling and electrophysiology . Direct evidence for this assumption has recently been provided with extracellular calcium transients measured in rabbit ventricle by the dye method (Hilgemann and Langer, 1984). The loss of post-stimulatory potentiation at individual excitations was associated with a net increment of extracellular calcium several times greater than the net influx found during individual rapid stimulations .…”