MECHANOTRANSDUCTION IN COLONIC SMOOTH-MUSCLE CELLS

We evaluated mechanisms which mediate alterations in intracellular bio chemical events in response to transient mechanical stimulation of col onic smooth muscle cells. Cultured myocytes from the circular muscle l ayer of the rabbit distal colon responded to brief focal mechanical de formation of the plasma membrane with a transient increase in intracel lular calcium concentration ([Ca2+](i)) with peak of 422.7 +/- 43.8 nM above an average resting [Ca2+](i) of 104.8 +/- 10.9 nM (n = 57) foll owed by both rapid and prolonged recovery phases. The peak [Ca2+](i) i ncrease was reduced by 50% in the absence of extracellular Ca2+, while the prolonged [Ca2+](i) recovery was either abolished or reduced to l ess than or equal to 15% of control values. In contrast, no significan t effect of gadolinium chloride (100 mu M) or lanthanum chloride (25 m u M) on either peak transient or prolonged [Ca2+](i) recovery was obse rved. Pretreatment of cells with thapsigargin (1 mu M) resulted in a 2 5% reduction of the mechanically induced peak [Ca2+](i) response, whil e the phospholipase C inhibitor U-73122 had no effect on the [Ca2+](i) transient peak. [Ca2+](i) transients were abolished when cells previo usly treated with thapsigargin were mechanically stimulated in Ca2+-fr ee solution, or when Ca2+ stores were depleted by thapsigargin in Ca2-free solution. Pretreatment with the microfilament disrupting drug cy tochalasin D (10 mu M) or microinjection of myocytes with an intracell ular saline resulted in complete inhibition of the transient. The effe ct of cytochalasin D was reversible and did not prevent the [Ca2+](i) increases in response to thapsigargin. These results suggest a communi cation, which may be mediated by direct mechanical Link via actin fila ments, between the plasma membrane and an internal Ca2+ store.