ryanodine and dodecyl-sulfate

A system for rapid superfusion with simultaneous measurement of contractile amplitude of single adult rat and rabbit ventricular cells is used to measure cellular response to alterations of the superfusate achieved in less than 0.3 s. The time course of contractile response of the cells to extracellular Ca concentration [( Ca]o) depletion and repletion identifies "fast" and "slow" cellular pools of Ca that contribute to contraction. The fast pool can be totally depleted or repleted within a single diastolic period. Depletion of this pool completely eliminates contraction in both rat and rabbit cell. Experiments using dimethonium to investigate the effect of Ca in the diffuse double layer and dodecyl sulfate to specifically augment sarcolemmal fixed-negative charge indicate that sarcolemmal binding sites may represent a major fraction of the fast pool. At 1 mM [Ca]o, this pool is functionally saturated in the rat but not nearly saturated in the rabbit. After 10 min Ca depletion more than 60 s of Ca repletion are required to restore full contraction amplitude. This indicates the presence of a slow pool of Ca that contributes to contraction. This pool, at 1 mM [Ca]o, is nearly functionally saturated in the rabbit but not nearly so in the rat. The responses to Ca depletion and repletion, Na depletion and repletion, and 1 microM ryanodine indicate that the contribution of Ca to contraction from the slow pool is much greater in the rat than in the rabbit and that its cellular locus is probably the sarcoplasmic reticulum.

Topics: Animals; Calcium; Male; Myocardial Contraction; Myocardium; Rabbits; Rats; Rats, Inbred Strains; Ryanodine; Sarcolemma; Sodium; Sodium Dodecyl Sulfate

The anionic amphiphile dodecyl sulfate was used at the concentration of 100 microM, below the concentration at which membrane permeability is compromised. In rat myocardial tissue culture dodecyl sulfate induced a large increase in Ca uptake in the intact cells, of which 84% was distributed in a rapidly exchangeable (t1/2 less than 18 s) and 16% in a slowly exchangeable (t1/2 = 17 min) compartment. Dodecyl sulfate induced a large increase in Ca bound to isolated sarcolemmal membrane of these cells. This increase in membrane binding and the distribution in whole cells is consistent with insertion of dodecyl sulfate in the sarcolemma (SL) with subsequent Ca binding to its anionic head group. With perfusate extracellular calcium concentration ([Ca]o) equal to 1 mM, dodecyl sulfate produced greater than 60% increase in active force in ventricular tissue from adult rabbit and neonatal rat but virtually no increase in adult rat ventricle. Preperfusion with 0.1 mM [Ca]o or 10(-6) M ryanodine markedly increased the relative response of adult rat ventricle to dodecyl sulfate. After a quiescent period in rabbit ventricle, dodecyl sulfate caused a progressive increase of force of each beat compared with control; i.e., the treppe response was increased at each successive beat. This did not occur in adult rat ventricle. These results further clarify the different quantitative role of SL-bound versus sarcotubular Ca in the hearts of different species.

Topics: Age Factors; Alkaloids; Animals; Calcium; Heart; Myocardial Contraction; Myocardium; Rabbits; Rats; Ryanodine; Sarcolemma; Sodium Dodecyl Sulfate; Tissue Distribution