Isolated rat glomerular cells demonstrate L-type Ca(2+)-channel activity.
The presence of L-type calcium (Ca2+)-channels and the effects of Ca(2+)-channel antagonists on cells of rat glomeruli were investigated. Glomeruli were isolated by graded sieving and after preincubation (10 min) in zero Ca2+, the uptake of 45Ca2+ by glomerular cells was measured. Depolarization with KCl (50 mM) or the dihydropyridine agonist Bay K 8644 (10 microM) stimulated 45Ca2+ uptake by 13% and 24%, respectively, above control (100%), which was inhibited by nifedipine (Nif, 10 microM), P < 0.05, and by both S and R isomers of verapamil (Ver, 10 microM), P < 0.001. In a separate experimental preparation, isolated glomeruli were preloaded (45 min) with 45Ca2+. Following a 45 min perifusion (37 degrees C, CaCl2 1.26 mM, in the absence of 45Ca2+), both KCl (50 mM) and Bay K 8644 (10 microM) induced cellular 45Ca2+ efflux with peak values above control of 11% and 15%, respectively, (P < 0.05). Exposure to Bay K 8644 preceded by depolarization with KCl resulted in enhanced 45Ca2+ efflux identifying the presence of voltage-dependent Ca(2+)-channel activity. Cultured rat mesangial cells grown to confluence on coverslips were preloaded with Fura-2 and cytosolic Ca2+ was measured by microfluorometry. KCl (50 mM), gramicidin (2 microM) and/or Bay K 8644 (6 microM) stimulated Ca2+ influx which was inhibited by Ver (10 microM). Ver did not alter endothelin-stimulated Ca2+ signalling. We conclude that L-type Ca2+ channels are present on both rat glomerular (endothelial and/or mesangial) cells in vivo and on cultured mesangial cells, and their activation may be hormone specific.
McDermott
G F
GF
Department of Medicine, University of Toronto, Ontario, Canada.
Hurst
R D
RD
Whiteside
C I
CI
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism; D006096:Gramicidin / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D007678:Kidney Glomerulus / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D006096:Gramicidin; D011189:Potassium Chloride; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D014700:Verapamil; D002118:Calcium