Separation of two pathways for calcium entry into chromaffin cells.
1. The effects of various drugs on 45Ca + 40Ca uptake into cultured bovine adrenal chromaffin cells evoked by 1,1-dimethyl-4-phenylpiperazinium (DMPP) or high K, were studied. In the presence of 1 mM external 40Ca, with 45Ca as a radiotracer, unstimulated cells took up an average of 0.13 fmol/cell 40Ca and 772 c.p.m./10(6) cells of 45Ca (n = 76). Upon stimulation with DMPP (100 microM for 60 s) or K (59 mM for 60 s), Ca uptake increased to 0.92 and 1 fmol/cell, respectively. 2. Flunarizine behaved as a potent blocker of both DMPP- and K-evoked Ca uptake (IC50 of 1.76 and 1.49 microM, respectively for DMPP and K). A similar picture emerged with Cd ions, though Cd exhibited an IC50 against K (1.86 microM) slightly lower than the IC50 against DMPP (8.14 microM). 3. Clear cut differences were observed with amiloride, guanethidine, nimodipine and nisoldipine which behaved as selective blockers of DMPP-mediated Ca uptake responses: IC50 values to block DMPP effects were 290, 27, 1.1 and 1.63 microM respectively for amiloride, guanethidine, nimodipine and nisoldipine. Amiloride blocked K-evoked Ca uptake by only 35% and guanethidine did not affect it. Nisoldipine inhibited K-evoked Ca uptake only partially at low concentrations (about 30%); a second blocking component was observed at the highest concentration used (10 microM). At 10 microM, nimodipine blocked K-evoked Ca uptake by 50%. 4. Thus, it seems that the nicotinic receptor mediated Ca uptake pathway can be pharmacologically separated from the K-activated pathway. The results are compatible with the hypothesis that in cultured bovine adrenal chromaffin cells, stimulation of nicotinic receptors recruits a single type of Ca channel which is sensitive to flunarizine, Cd, amiloride, guanethidine, nimodipine and nisoldipine. The results also suggest that K depolarization might be recruiting in addition to this channel, another Ca channel which is highly sensitive to Cd and flunarizine, resistant to nisoldipine, nimodipine and amiloride, and insensitive to guanethidine.
Gandía
L
L
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Casado
L F
LF
López
M G
MG
García
A G
AG
D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002417:Cattle; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D005444:Flunarizine / Q000494:pharmacology; D006145:Guanethidine / Q000494:pharmacology; D066298:In Vitro Techniques; D009553:Nimodipine / Q000494:pharmacology; D015737:Nisoldipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000187:drug effects
D015220:Calcium Channels; D002132:Calcium Radioisotopes; D011978:Receptors, Nicotinic; D002104:Cadmium; D015737:Nisoldipine; D004246:Dimethylphenylpiperazinium Iodide; D009553:Nimodipine; D000584:Amiloride; D005444:Flunarizine; D011188:Potassium; D006145:Guanethidine