alpha 1B N-type calcium channel isoforms with distinct biophysical properties.

N-type calcium channels both generate the initial calcium signal to trigger neurotransmitter release and also interact with synaptic release proteins at many mammalian central nervous system synapses. Two isoforms of the alpha 1B N-type channel from rat brain (alpha 1B-I and alpha 1B-II) were found to differ in four regions: (1) a glutamate (Glu) to glycine (Gly) substitution in domain I S3; (2) a Gly to Glu substitution in the domain I-II linker; (3) the insertion or deletion of an alanine (Ala) in the domain I-II linker; and (4) the presence or absence of serine/phenylalanine/methionine/glycine (SFMG) in the linker between domain III S3-S4. Comparison of the electrophysiological properties of the alpha 1B-I and alpha 1B-II N-type channels shows that they exhibit distinct kinetics as well as altered current-voltage relations. Utilizing chimeric alpha 1B-I and alpha 1B-II cDNAs, we show that: (1) the Glu 177 to Gly substitution in domain I S3 increases the rate of activation by approximately 15-fold; (2) the presence or absence of Ala 415 in the domain I-II linker alters current-voltage relations by approximately 10 mV but does not affect channel kinetics; (3) the substitution of Gly 387 to Glu in the domain I-II linker also has no effect on kinetics; and (4) the presence or absence of SFMG (1236-1239) in domain III S3-S4 did not significantly affect channel current-voltage relations, kinetics, or steady state inactivation. We conclude that molecularly distinct alpha 1B isoforms are expressed in rat brain and may account for some of the functional diversity of N-type currents in native cells.