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Ca²⁺-ATPase-driven calcium accumulation in Ustilago maydis plasma membrane vesicles

Department of Agricultural Sciences, University of Bristol, AFRC Institute of Arable Crops Research, Long Ashton Research Station, Bristol BS18 9AF, UK

Author for correspondence: D. T. Cooke.

ABSTRACT

Ca²⁺transport has been measured across plasma membrane vesicles isolated from cells of Ustilago maydis. This transport was found to be ATP- (or to a lesser extent GTP) and Mg²⁺-dependent. Inconsistent release of Ca²⁺from intact vesicles was obtained using the calcium ionophore A23187. However, Ca²⁺was released by Triton X-100 in a concentration-dependent manner. Transport was inhibited by vanadate (>50%) and erythrosin B (about 50%), I50 being about 10 µM for both inhibitors. In the presence of the protonophores CCCP or gramicidin, partial inhibition of Ca²⁺transport (about 20%) was observed, but the Ca²⁺-channel blockers, nifedipine, diltiazem and verapamil had no effect, although the latter inhibited proton transport. The results indicate that Ca²⁺transport in U. maydis is regulated by a P-type ATPase with similar properties to that found in higher plants.