Acetylcholine-gated cation channels at the neuromuscular junction open in response to acetylcholine released by the nerve terminal and allow Na⁺ ions to enter the muscle cell, which causes membrane depolarization and ultimately leads to muscle contraction.

A. Patch-clamp measurements show that young rat muscles have cation channels that respond to acetylcholine (Figure Q11–4). How many kinds of channel are there? How can you tell?

B. For each kind of channel, calculate the number of ions that enter in one millisecond. (One ampere is a current of one coulomb per second; one pA equals 10^–12 ampere. An ion with a single charge such as Na⁺ carries a charge of 1.6 × 10^–19 coulomb.)

Transcribed Image Text:

2 pA 40 msec