L-type Ca2+ channel expression along feline smooth muscle oesophagus

Muscle from the proximal smooth muscle (SM) oesophagus of the cat demonstrates contractions of greater amplitude and greater sensitivity to cholinergic stimulation than muscle from the distal SM oesophagus. In the light of the central role of calcium influx in SM contractility, we hypothesized that regional differences in oesophageal contractility may be associated with differential expression of L-type calcium channels (L-Ca) along the SM oesophagus. L-Ca expression was compared between proximal and distal regions of the circular SM oesophagus by Western blots. Patch clamp technique was utilized to study L-Ca currents. Muscle strip studies assessed L-Ca contribution to contractile activity. The protein expression of L-Ca and L-Ca current density was greater in the proximal than distal region. L-Ca voltage and time-dependent activation and inactivation curves were similar in cells from both regions. Stimulation of muscle strips with acetylcholine (ACh) in the presence of tetrodotoxin resulted in contractions of greater amplitude in the proximal region. The L-Ca agonist Bay K 8644 caused a greater increase in ACh-induced contraction amplitude in muscle strips from the proximal region. Therefore, regional myogenic differences in L-Ca expression along the circular SM oesophageal body exist and may contribute to the nature of oesophageal contractions.