Abstract
We investigated the concentration- and Ca 2+-dependent effects of CaM mutants, CaM 12 and CaM 34, in which Ca 2+-binding to its N- and C-lobes was eliminated, respectively, on the Ca V1.2 Ca 2+ channel by inside-out patch clamp in guinea-pig cardiomyocytes. Both CaM 12 and CaM 34 (0.7–10 μM) applied with 3 mM ATP produced channel activity after “rundown”. Concentration–response curves were bell-shaped, similar to that for wild-type CaM. However, there was no obvious leftward shift of the curves by increasing [Ca 2+], suggesting that both functional lobes of CaM were necessary for the Ca 2+-dependent shift. However, channel activity induced by the CaM mutants showed Ca 2+-dependent decrease, implying a Ca 2+ sensor existing besides CaM. These results suggest that both N- and C-lobes of CaM are required for the Ca 2+-dependent regulations of Ca V1.2 Ca 2+ channels.
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