VOLTAGE-GATED CALCIUM CHANNELS AND NONVOLTAGE-GATED CALCIUM-UPTAKE PATHWAYS IN THE RAT INCISOR ODONTOBLAST PLASMA-MEMBRANE

Odontoblasts participate actively in the transport and accumulation of Ca2+ ions to the mineralization front during dentinogenesis. These ce lls are known to carry membrane-bound ATP-driven pumps and Na+/Ca2+ an tiports for Ca2+ extrusion, but little is known about Ca2+ influx mech anisms into these cells. It has been shown that the administration of Ca2+ channel blockers in vivo strongly impairs Ca2+ uptake in the mine ral phase during dentinogenesis in the rat; the present in vitro study is aimed at further elucidating odontoblast Ca2+ uptake mechanisms. D issected rat incisor odontoblasts exhibited a pronounced fluorescence when incubated with a fluorescently-labeled (STBodipy) dihydropyridine , which is specific for voltage-gated Ca2+ channels of the L-type, and this binding was competitively abolished by nifedipine. As assayed by fluorescence spectrometry, odontoblast Ca2+ uptake was enhanced by th e agonistic dihydropyridine BAYK-8644 (5 mu M) as well as by plasma me mbrane depolarization in a high K+ (120 mM) medium. The Ca2+ uptake af ter depolarization was impaired by nifedipine (5 mu M). When treated w ith the Ca2+-ATPase inhibitor cyclopiazonic acid (CPA; 10 mu M), a non voltage-gated uptake of Ca-45(2+) was identified. This uptake was not influenced by nifedipine (20 mu M) but was impaired by lanthanum ions (200 mu M). A nonvoltage-gated uptake of Mn2+ into CPA-treated cells c ould be traced using the fura-2 quenching technique. This CPA-induced Ca2+ flux was not caused by an alteration of the plasma membrane poten tial, as assayed with di-8-ANEPPS. The results demonstrate that Ca2+ f lux into dentinogenically active odontoblasts occurs through voltage-g ated Ca2+ channels of the L-type and by nonvoltage-gated, agonist-sens itive Ca2+ uptake pathways.