Mechanotransduction in Colonic Smooth Muscle Cells

We evaluated mechanisms which mediate alterations in intracellular biochemical events in response to transient mechanical stimulation of colonic smooth muscle cells. Cultured myocytes from the circular muscle layer of the rabbit distal colon responded to brief focal mechanical deformation of the plasma membrane with a transient increase in intracellular 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) followed by both rapid and prolonged recovery phases. The peak Ca²⁺] _i increase was reduced by 50% in the absence of extracellular Ca²⁺, while the prolonged Ca²⁺] _i recovery was either abolished or reduced to ≤15% of control values. In contrast, no significant effect of gadolinium chloride (100 μm) or lanthanum chloride (25 μm) on either peak transient or prolonged Ca²⁺] _i recovery was observed. Pretreatment of cells with thapsigargin (1 μm) resulted in a 25% reduction of the mechanically induced peak Ca²⁺] _i response, while the phospholipase C inhibitor U-73122 had no effect on the Ca²⁺] _i transient peak. Ca²⁺] _i transients were abolished when cells previously treated with thapsigargin were mechanically stimulated in Ca²⁺-free solution, or when Ca²⁺ stores were depleted by thapsigargin in Ca²⁺-free solution. Pretreatment with the microfilament disrupting drug cytochalasin D (10 μm) or microinjection of myocytes with an intracellular saline resulted in complete inhibition of the transient. The effect of cytochalasin D was reversible and did not prevent the Ca²⁺] _i increases in response to thapsigargin. These results suggest a communication, which may be mediated by direct mechanical link via actin filaments, between the plasma membrane and an internal Ca²⁺ store. Received: 24 March 1997/Revised: 21 July 1997