Segmentally distinct effects of depolarization on intracellular [Ca2+] in renal arterioles.
Experiments were performed to determine the influence of depolarization on intracellular Ca2+ concentration ([Ca2+]i) in renal arterioles and the possible role of voltage-gated Ca2+ channels in these responses. Glomeruli with attached arterioles and thick ascending limb were dissected from rabbit kidney and loaded with fura 2. [Ca2+]i of nonperfused arterioles was monitored using a microscope-based dual-excitation wavelength spectrofluorometry system. Afferent arteriolar [Ca2+]i averaged 150 +/- 11 nM (n = 20) when bathed in Ringer solution containing 1.5 mM Ca2+ and 5 mM K+. Replacement of the normal Ringer solution with one containing 100 mM K+ significantly increased afferent arteriolar [Ca2+]i to 196 +/- 12 nM. This response was abolished in the absence of extracellular Ca2+. In the presence of 1 microM nifedipine, 100 mM K+ elicited a 10% decrease in afferent arteriolar [Ca2+]i (P < 0.05). Thus nifedipine reversed the afferent [Ca2+]i response to depolarization, implicating voltage-gated Ca2+ channels as the influx pathway. In contrast to the behavior of afferent arterioles, the 100 mM K+ solution reduced efferent arteriolar [Ca2+]i from 188 +/- 17 to 148 +/- 13 nM (n = 11, P < 0.01), an effect that was not influenced by nifedipine. These observations support a role for voltage-gated Ca2+ channels in eliciting depolarization-induced increases in afferent arteriolar [Ca2+]i while failing to provide evidence for operation of such a mechanism at efferent arteriolar sites.
Carmines
P K
PK
Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Fowler
B C
BC
Bell
P D
PD
D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D007678:Kidney Glomerulus / Q000098:blood supply*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012079:Renal Circulation; D013997:Time Factors
D009543:Nifedipine; D011188:Potassium; D002118:Calcium