Dihydropyridine- and omega-conotoxin-resistant, neomycin-sensitive calcium channels mediate the depolarization-induced increase in internal calcium levels in cortical slices from immature rat brain

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 261; no. 1; pp. 324 - 330
• Main Authors: Perrier, M L, Scatton, B, Benavides, J
• Format: Journal Article
• Language: English
• Published: United States American Society for Pharmacology and Experimental Therapeutics 01.04.1992
• Subjects: Aminoglycosides; Animals; Anti-Bacterial Agents - pharmacology; Brain - drug effects; Brain - metabolism; Calcium - metabolism; Calcium Channel Blockers - pharmacology; Female; Fura-2 - metabolism; Male; Potassium Chloride - pharmacology; Rats; Rats, Inbred Strains
• ISSN: 0022-3565; 1521-0103

In order to characterize pharmacologically voltage-operated calcium channels in the rat brain, we have developed a technique to measure intracellular calcium levels ([Ca++]i) in immature rat cortical slices loaded with the fluorescent calcium probe Fura-2. KCl depolarization caused a rapid and reversible increase in cortical [Ca++]i. A significant increase was already observed at 20 mM KCl and the maximal effect was obtained at 77 mM. This response was not modified when extracellular Na+ was substituted by the nonpermeant cation bis(2-hydroxyethyl)-dimethylammonium chloride and was insensitive to the Na+ channel blocker tetrodotoxin (1 microM). In the absence of extracellular Ca++, KCl (50 mM) failed to increase [Ca++]i. The KCl (50 mM)-induced increase in [Ca++]i was not affected by the L-type calcium channel blockers nifedipine and isradipine and was only partially inhibited (by less than 30% at 50 microM) by verapamil and diltiazem. In contrast, nimodipine prevented this response by 41% at 50 microM. Flunarizine (a nonselective T channel blocker) inhibited the KCl response by 47% at 30 microM, whereas nicergoline (another nonselective T channel blocker) reduced this entry by 74% at 300 microM (IC50 = 120 microM). Cyclandelate, an atypical calcium antagonist, inhibited KCl-induced increase in [Ca++]i with a maximal effect of 41% at 30 microM, whereas perhexiline was inactive. The KCl-induced rise in [Ca++]i was only marginally inhibited by omega-conotoxin with a maximal effect of 20% from 1 nM to 1 microM.