We previously demonstrated that upregulation of intermediate-conductance Ca(2+)-activated K(+) channels (K(Ca)3.1) is necessary for mitogen-induced phenotypic modulation in isolated porcine coronary smooth muscle cells (SMCs). The objective of the present study was to determine the role of K(Ca)3.1 in the regulation of coronary SMC phenotypic modulation in vivo using a swine model of postangioplasty restenosis.