Beta-adrenergic effects on cellular Na, Mg, Ca, K and Cl in vascular smooth muscle: electron probe analysis of rabbit pulmonary artery.

The effects of beta-adrenergic stimulation on the cellular content and subcellular distribution of Na, Mg, Ca, K and Cl were determined by electron probe X-ray microanalysis of muscles stimulated with 5-hydroxytryptamine. Isoproterenol caused a significant decrease in cytoplasmic and mitochondrial Na and Cl, and an increase in cytoplasmic Mg. Isoproterenol also significantly decreased total cytoplasmic Ca measured with small diameter probes, without affecting cellular Ca measured with large probes that included the sarcoplasmic reticulum (SR). The decrease in cytoplasmic Na and the effects on cytoplasmic and cellular Ca are consistent with, respectively, beta-adrenergic stimulation of the Na-pump and of Ca-uptake into the SR, but the beta-adrenergic increase in cytoplasmic Mg also raises the possibility of stimulated Na/Mg exchange.