Cholinergic effects on intracellular free calcium concentration in renal corpuscle: role of parietal sheet.
To investigate a possible effect of cholinergic agonists on the renal glomerular function, fura-2 microfluorometric measurements of intracellular free calcium [( Ca2+]i) were performed on single intact glomeruli, single isolated parietal sheets of the Bowman's capsule and single parietal sheet-deprived glomeruli (PS-D glomerulus). Carbachol (10(-4) M), in the presence of 2 mM external calcium, induced a biphasic increase in [Ca2+]i characterized by a sharp initial peak followed by a sustained plateau in the whole glomerulus (delta [Ca2+]i = 177 +/- 13 and 70 +/- 7 nM, respectively; n = 21) and in the parietal sheet (418 +/- 30 and 111 +/- 13 nM, respectively; n = 21). In the PS-D glomerulus (n = 9), the response was less marked and included a barely visible peak (77 +/- 13 nM) and a relatively low plateau (49 +/- 11 nM). In the absence of external calcium, the peak phase was preserved in the three structures, indicating a calcium release from intracellular pools, whereas the plateau, due to the entry of external calcium, was suppressed. These effects were fully inhibited by 10(-4) M of either atropine or pirenzepine, demonstrating the muscarinic nature of the receptors. Dose-response curves showed that the parietal sheet was more sensitive to the physiological agonist (acetylcholine) than to carbachol. A still unexplained difference in sensitivity was noted between peak and plateau, respectively (half-maximal responses were 5 x 10(-6) vs. 5 x 10(-7) M for carbachol and 2 x 10(-7) vs. 3 x 10(-8) M for acetylcholine).(ABSTRACT TRUNCATED AT 250 WORDS)
Lebrun
F
F
Laboratoire de Physiologie Cellulaire, Unité de Recherche Associée 219, Centre National de la Recherche Scientifique, Collège de France, Paris.
Morel
F
F
Vassent
G
G
Marchetti
J
J
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006652:Histological Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D007678:Kidney Glomerulus / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D010277:Parasympathomimetics / Q000494:pharmacology*; D010890:Pirenzepine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011950:Receptors, Cholinergic / Q000378:metabolism
D010277:Parasympathomimetics; D011950:Receptors, Cholinergic; D010890:Pirenzepine; D001285:Atropine; D002217:Carbachol; D000109:Acetylcholine; D002118:Calcium