Functional receptor-channel coupling compared in contractile and proliferative human vascular smooth muscle

We have previously identified a human vascular smooth muscle clone that can reversibly convert between proliferative and contractile phenotypes. Here we compared receptor-channel coupling in these cells using fura-2 to monito r [Ca2+](i) and patch-clamp to record currents. Histamine elevated [Ca2+](i ) in all cells and caused contraction of cells exhibiting the contractile p henotype. The rise of [Ca2+](i) persisted in Ca2+-free solution and was abo lished by thapsigargin, indicating involvement of stores. Whole cell electr ophysiological recording revealed that histamine evoked transient outward K + current, indicating functional receptor-channel coupling. The time-course and amplitude of the histamine-activated current were similar in cells of the proliferative and contractile phenotypes. Moreover, a large conductance K+ channel was recorded in cell-attached patches and was activated by hist amine as well as the Ca2+ ionophore A-23187, identifying it as the large co nductance Ca2+-dependent K+ channel. This K+ channel showed similar charact eristics and activation in both proliferative and contractile phenotypes, i ndicating that expression was independent of phenotype. In contrast, histam ine also elicited an inward Cl- current in some contractile cells, suggesti ng differential regulation of this current depending on phenotype. These st udies demonstrate the usefulness of this human Vascular cell clone for stud ying functional plasticity of smooth muscle, while avoiding complications a rising from extended times in culture. (C) 2007 Wiley-Liss, Inc.