(Na) sub i modulates isoproterenol's effect on Ca permeability in cultured heart cells

Journal Article · Sat Aug 01 00:00:00 EDT 1987 · American Journal of Physiology; (USA)

OSTI ID:5030459

Kim, D; Smith, T W ^[1]

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1. Harvard Medical School, Boston, MA (USA)

Isoproterenol (ISO) augments the slow inward Ca current in cardiac muscle cells. The authors examined the role of intracellular Na (Na{sub i}) on ISO-mediated alterations in Ca uptake in cultured chick heart cells. In 140 mM Na medium, 1 {mu}M ISO did not measurably alter {sup 45}Ca uptake. When cells were first preincubated in Na-free medium for 5 min and then incubated in control medium with {sup 45}Ca, ISO increased {sup 45}Ca uptake by 30%. Nifedipine, verapamil, or dl-propranolol abolished the effect of ISO on {sup 45}Ca uptake. CGP 28392, a Ca channel agonist, increased Ca influx in a manner that was augmented by decreased Na{sub i}, similar to the ISO response. Neither ISO nor CGP 28392 altered {sup 45}Ca uptake when cells preincubated in Na-free medium were further incubated in Na-free medium containing {sup 45}Ca. Exposure of cells to Na-free medium or 25 mM K{sup +} medium caused depolarization of the resting membrane potential to approximately {minus}40 mV. In the absence of ISO, the {sup 45}Ca uptake in cells preincubated in Na-free or 25 mM extracellular K (K{sub o}) medium was significantly greater than in cells preincubated in control medium. This appeared to be due partly to increased {sup 45}Ca uptake via nifedipine-sensitive pathways. These findings support the hypothesis that reduction in Na{sub i} concentration ((Na){sub i}) enhances the ISO-induced augmentation of Ca uptake via nifedipine-sensitive pathways (presumably via slow Ca channels), probably by a direct effect on the channels.

• OSTI ID: 5030459
• Journal Information: American Journal of Physiology; (USA), Vol. 253:2; ISSN 0002-9513
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
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