Transfer of L-type calcium channel IVS6 segment increases phenylalkylamine sensitivity of alpha(1A)

Conditioned (''use-dependent'') inhibition by phenylalkylamines (PAAs) is a characteristic property of L-type calcium (Ca2+) channels. To determine the structural elements of the PAA binding domain we transferred sequence stretches of the pore-forming regions of repeat III and/or IV from the skeletal muscle alpha(1) subunit (alpha(1S)) to the class A alpha(1) subunit (alpha(1A)) and expressed these chimeras together with beta(1a) and alpha(2)/delta subunits in Xenopus oocytes. The corresponding barium currents (I-Ba) were tested for PAA sensitivity during trains of depolarizing test pulses (conditioned block). I-Ba of oocytes expressing the alpha(1A) subunit were only weakly inhibited by PAAs (less than 10% conditioned block of I-Ba during a 100-ms pulse train of 0.1 Hz). Transfer of the transmembrane segment IVS6 from alpha(1S) to alpha(1A) produced an enhancement of PAA sensitivity of the resulting alpha(1A)/alpha(1S) chimera comparable to L-type alpha(1) subunits (about 35% conditioned block of I-Ba during a 100-ms pulse train of 0.1 Hz). Our results demonstrate that substitution of 11 amino acids within the segment IVS6 of alpha(1A) with the corresponding residues of alpha(1S) is sufficient to transfer L-type PAA sensitivity into the low sensitive class A Ca2+ channel.