Differential regulation of Ca2+-activated Cl− currents in rabbit arterial and portal vein smooth muscle cells by Ca2+-calmodulin-dependent kinase
Corresponding author I. Greenwood: Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, London, UK., Email: email@example.com
- 1Ca2+-activated chloride currents (ICl(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.
- 2In 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 μm evoked well sustained, outwardly rectifying ICl(Ca) currents in about 90 % of cells. The CaMKII inhibitor KN-93 (5 μm) increased the amplitude of ICl(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.
- 3In 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 ICl(Ca) evoked by 500 nm Ca2+.
- 4In PV myocytes, ICl(Ca) was evoked by pipette solutions containing up to 1 μm free Ca2+ in less than 40 % of cells. Application of KN-93 to cells where ICl(Ca) was sustained produced a small inhibition (≈25 %) of the current in 70 % of the cells.
- 5The present study shows that regulation of Ca2+-dependent Cl− channels by CaMKII differs between arterial and portal vein myocytes.