cGMP‐dependent protein kinase decreases calcium sensitivity of skinned cardiac fibers

Abstract

Chemically skinned (Lubrol WX) cardiac muscle fibres produce half-maximum isometric tension at pCa 6.18 (pH 6.7) in presence of MgATP (10 mM). After addition of cGMP (5 μM) and cGMP-depenent protein kinase (0.1 μM), the pCa required for half-maximum activation is 5.96, while maximum tension is not affected. Similar shifts in the tension/pCa-relationship have been observed after incubation of skinned cardiac muscle fibres with cAMP of catalytic subunit of the cAMP-dependent protein kinase. The shift in the Ca²⁺-sensitivity is associated with an increased incorporation of radioactivity into a M _r 28 000 band (presumably troponin-I) and a M _r 145 000 band.