Hyperpolarization-activated cationic channels in smooth muscle cells are stretch sensitive

Area of Science:

• Physiology
• Cell Biology
• Biophysics

Background:

• Smooth muscle cells possess ion channels crucial for regulating cellular function.
• Hyperpolarization-activated channels and stretch-activated channels (SACs) are known to exist in various cell types.
• Understanding channel properties is key to elucidating cellular responses to stimuli.

Purpose of the Study:

• To investigate the properties of hyperpolarization-activated channels in toad stomach smooth muscle cells.
• To determine if these channels are influenced by mechanical stretch.
• To characterize the ion permeation and conductance of these channels.

Main Methods:

• Patch-clamp technique was employed on single smooth muscle cells from the toad stomach.
• Cell-attached patches were subjected to hyperpolarizing voltage pulses.
• Mechanical stretch was applied to the cell-attached patches using suction.

Main Results:

• Hyperpolarization-activated channels (HA-SACs) were identified, activated by potentials more negative than -60 mV.
• Channel activity increased and latency decreased with increasing hyperpolarization.
• Mechanical stretch also increased HA-SAC activity and shortened activation latency.
• HA-SACs were present in 83% of patches and showed properties similar to previously described SACs.
• Ion permeation studies revealed currents carried by Na+ and K+, with amplitude modulated by ion concentrations and divalent cations.

Conclusions:

• Hyperpolarization- and stretch-activated channels (HA-SACs) are present in toad stomach smooth muscle.
• These channels exhibit dual gating by both membrane potential and mechanical stretch.
• HA-SACs likely represent a subset of stretch-activated channels, demonstrating a functional link between mechanical and electrical stimuli.