Effects of a physiological insulin concentration on the endothelin-sensitive Ca2+ store in porcine coronary artery smooth muscle.
The effect of insulin to attenuate the Ca2+ and contractile response of vascular smooth muscle to a number of agonists has been described previously, but the Ca2+ regulatory mechanisms of insulin action remain unclear. We determined the effect of a physiological insulin concentration (300 pmol/l) on the Ca2+ response of vascular smooth muscle cells of the porcine right coronary artery to endothelin 1 (ET-1); furthermore, we examined the cellular Ca2+ stores affected by insulin (i.e., Ca2+ stores releasable by inositol 1,4,5-trisphosphate, caffeine, and ionomycin). We measured the Ca2+ responses of acutely isolated single smooth muscle cells with the fluorescent Ca2+ indicator Fura-2. Acute insulin exposure (20 min) significantly attenuated the Ca2+ response of single smooth muscle cells to 10 nmol/l ET-1. This inhibitory effect of insulin was observed both in the presence and absence of extracellular Ca2+. In contrast with the effects on ET-1-induced Ca2+ responses, insulin did not inhibit the Ca2+ response to 5 mmol/l caffeine, an agent that directly releases sarcoplasmic reticulum Ca2+ stores. Insulin was also without effect on the total cellular Ca2+ store released by 1 micromol/l ionomycin, a Ca2+-transporting ionophore. When ET-1 and caffeine were given in succession, a sizable caffeine-sensitive Ca2+ store could be released from insulin-treated cells but not control cells, indicating that the sarcoplasmic reticulum Ca2+ store of insulin-treated cells was not depleted by ET-1. Generalized depletion of the sarcoplasmic reticulum Ca2+ store is not one of the cellular mechanisms involved in the effect of insulin on coronary smooth muscle; instead, the effect may be due to an inhibitory influence on transmembrane signal transduction, such as diminished ET-1-induced inositol 1,4,5-trisphosphate production or reduced ability of this phosphoinositol to release stored Ca2+.
Dick
G M
GM
Vascular Biology Laboratory, Dalton Cardiovascular Research Center, University of Missouri, Columbia 65211, USA.
Sturek
M
M
D000704:Analysis of Variance; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000187:drug effects / Q000378:metabolism*; D016232:Endothelins / Q000494:pharmacology*; D016257:Fura-2; D007328:Insulin / Q000494:pharmacology* / Q000502:physiology; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013552:Swine
D016232:Endothelins; D007328:Insulin; D002110:Caffeine; D002118:Calcium; D016257:Fura-2