Does muscle activation occur by direct mechanical coupling of transverse tubules to sarcoplasmic reticulum?

Our knowledge of the physiological and biochemical constituents of skeletal muscle excitation has increased greatly during the last few years but this has not led to a consensus of the physiological mode of muscle activation. Three hypotheses of transmission, involving either transmitter-receptor interaction or direct mechanical coupling, are still under active consideration. The hypothesis of direct mechanical coupling currently being evaluated proposes that the dihydropyridine receptor in the transverse tubules serves as a voltage sensor that communicates directly with the junctional foot protein/Ca2+ channel of sarcoplasmic reticulum to initiate opening of the channel.