A new method for assessing Ca2+ requirements for vasoconstriction in the rat isolated perfused kidney. Effect of...

The consecutive perfusion with three different media containing 1) a high-K+, Ca(2+)-free solution with 1 mM of EDTA, 2) a high-K+, Ca(2+)-free solution with 1mM of EDTA and 0.3-10 microM of norepinephrine (NE) or 1-10 nM of endothelin (ET), and 3) a normal K+ solution without EDTA, NE, or ET, respectively, produced three rapid and transient vasoconstrictions of the isolated and perfused rat kidney. Results obtained from preincubation with prazosin (0.9 nM) and nifedipine (10 nM) or reperfusion at various Ca2+ concentrations showed that the responses involved are characterized by a different mobilization of cellular and extracellular Ca2+. The first phase greatly depends on the influx of extracellular Ca2+ and/or membrane Ca2+ through voltage-dependent channels, the second from mobilization of intracellular Ca2+, while the third is due mainly to the influx of extracellular Ca2+ through receptor-activated channels. NE elicited Ca2+ mobilization from both cellular and extracellular sources through activation of alpha-1 adrenoceptors. ET is particularly effective in producing extracellular Ca(2+)-dependent vasoconstriction in a prazosin-resistant manner. Present results show that this method could be suitable to distinguish different Ca2+ requirements for spasmogen-induced vasoconstriction in the isolated and perfused rat kidney.