Shortening velocity and myosin heavy- and light-chain isoform mRNA in rabbit arterial smooth muscle cells

Abstract

In smooth muscle cells (SMCs) isolated from rabbit carotid, femoral, and saphenous arteries, relative myosin isoform mRNA levels were measured in RT-PCR to test for correlations between myosin isoform expression and unloaded shortening velocity. Unloaded shortening velocity and percent smooth muscle myosin heavy chain 2 (SM2) and myosin light chain 17b (MLC17b) mRNA levels were not significantly different in single SMCs isolated from the luminal and adluminal regions of the carotid media. Saphenous artery SMCs shortened significantly faster ( P < 0.05) than femoral SMCs and had more SM2 mRNA ( P < 0.05) than carotid SMCs and less MLC17b mRNA ( P < 0.001) and higher tissue levels of SMB mRNA ( P < 0.05) than carotid and femoral SMCs. No correlations were found between percent SM2 and percent MLC17b mRNA levels and unloaded shortening velocity in SMCs from these arteries. We have previously shown that myosin heavy chain (MHC) SM1/SM2 and SMA/SMB and MLC17a/MLC17bisoform mRNA levels correlate with protein expression for these isoforms in rabbit smooth muscle tissues. Thus we interpret these results to suggest that 1) SMC myosin isoform expression and unloaded shortening velocity do not vary with distance from the lumen of the carotid artery but do vary in arteries located longitudinally within the arterial tree, 2) MHC SM1/SM2 and/or MLC17a/MLC17b isoform expression does not correlate with unloaded shortening velocity, and 3) intracellular expression of the MHC SM1/SM2 and MLC17a/MLC17b isoforms is not coregulated.