Action of Cholinergic Drugs on Accumulation of Tpmp⁺ on Human Spermatozoa

Abstract

Neurotransmitters or antagonists with nicotinic- or acetylcholine-type receptors were utilized to measure the accumulation of the radiolabeled lipophilic cation triphenyimethylphosphonium (TPMP⁺) on the plasma membrane of human sperm. Washed sperm incubated in the presence of TPMP⁺ in a low-K⁺ or high-K⁺ medium were allowed to take up the cation to a steady state (i.e., 20 min at 37°C). The difference between TPMP⁺ in each incubation medium was inserted in the Nernst equation yielding a resting membrane potential of -69 ± 2 mV. The addition of nicotine or acetylcholine to the low-K⁺ and high-K⁺ medium induced a hyperpolarization of 17% and 20%, respectively. In the presence of propranolol the membrane potential decreased by 44%. The association of nicotinic or acetylcholine receptor on human sperm or adrenergic β-receptor blocking agent may alter the ionic permeability of the membrane, possibly due to hyperpolarization or depolarization.

Key Words:

• Receptors
• Triphenylmethylphosphonium
• Nernst equation
• Membrane potential