Differential regulation of Ca 2+-activated Cl- currents in rabbit arterial and portal vein smooth muscle cells by Ca2+-calmodulin-dependent kinase

1. Ca2+-activated chloride currents (I-Cl(Ca)) were recorded from smooth muscle cells isolated from rabbit pulmonary (PA) and coronary artery (CA) as well as rabbit portal vein (PV). The characteristics and regulation by Ca2+-calmodulin-dependent kinase II (CaMKII) were compared between the three cell types. 2. In PA and CA myocytes dialysed and superfused with K+-free media, pipette solutions containing fixed levels of free Ca2+ in the range of 250 nM to 1 muM evoked well sustained, outwardly rectifying currents in about 90% of cells. The CaMKII inhibitor KN-93 (5 al) increased the amplitude of I-Cl(Ca) in PA and CA myocytes. However, the threshold intracellular Ca2+ concentration for detecting this effect was different in the two arterial cell types. KN-93 also enhanced the rate of activation of the time-dependent current during depolarising steps, slowed the kinetics of the tail current following repolarisation, and induced a negative shift of the steady-state activation curve. 3. In PA myocytes, the effects of KN-93 were not mirrored by its inactive analogue KN-92 but were reproduced by the inclusion of autocamtide-2-related CaMKII inhibitory peptide (ARIP) in the pipette solution. Cell dialysis with constitutively active CaMKII (30 nM) significantly reduced I-Cl(Ca) evoked by 500 nM Ca2+. 4. In PV myocytes, I-Cl(Ca) was evoked by pipette solutions containing up to 1 muM free Ca2+ in less than 40% of cells. Application of KN-93 to cells where I-Cl(Ca) was sustained produced a small inhibition (similar to 25 %) of the current in 70% of the cells. 5. The present study shows that regulation of Ca2+-dependent Cl- channels by CaMKII differs between arterial and portal vein myocytes.