In smooth muscle cells freshly isolated from the bovine ciliary body, effects of carbachol (CCh) on the membrane potential and current were examined by the whole-cell clamp method. The resting membrane potential of the muscle cells used was -60 +/- 1 mV (n = 111). Extracellular application of CCh (2 microM) depolarized the cells to -15 +/- 5 mV (n = 50) with an apparent increase in membrane conductance. Under voltage-clamp conditions, CCh (2 microM) evoked an inward current which exhibited inward-going rectification and reversed the polarity at about 0 mV. Removal of Na+ from the external solution caused a reduction of the amplitude of the current and a shift of the reversal potential to the negative direction. CCh was able to elicit an inward current even under a condition where Ca2+ was the only cation producing an inwardly directed electrochemical gradient. The current was not affected by verapamil or by tetrodotoxin. The CCh-induced current was inhibited by antimuscarinic agents with the affinity sequence: atropine approximately 4-DAMP > > pirenzepine > AF-DX116, indicating that the response is mediated by a muscarinic cholinoceptor that belongs to the M3-subtype. Unlike the non-selective cation channel current in intestinal smooth muscles, which is activated by elevation of the intracellular Ca2+ concentration ([Ca2+]i), the current of the ciliary muscle was inactivated when the [Ca2+]i was increased. The conductance, which admits Ca2+, may serve as a pathway for Ca2+ entry required for contraction.

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Nine cases of esotropia occurring in deprivation amblyopia, where exotropia rather than esotropia is usually found, showed a refractive error of hypermetropia. This fact suggested that an accommodative factor is largely responsible for the development of esotropia. A- or V-pattern strabismus was encountered in a higher incidence in deprivation amblyopia than in ordinary strabismus. Pattern-reversal VEP showed more prominent abnormality than flash VEP did. Studies of the sensitive period of the visual system revealed that the sensitivity is likely to be low for a month or two after birth and increases with a peak around the 18th month of age, decreasing thereafter with a waning slope to the end of the 8th year of life.