Extracellular acidity and ATP modulate ion currents in human cumulus cells indicating possible roles as metabolic sensors of the follicular microenvironment.

Cumulus cells (CCs), derived from granulosa cells, play a key role in supporting oocyte maturation and development through bidirectional communication. However, their electrophysiological properties in humans are poorly defined. Here, we characterized ionic currents and their modulation in primary human CCs obtained from patients undergoing in vitro fertilization. Whole cell patch-clamp recordings identified three electrophysiological sub-populations: CC-type 1, expressing voltage-dependent K+ currents supported mainly by potassium voltage-gated channel subfamily A member 5 (KV1.5, KCNA5); CC-type 2, predominantly showing a barium-sensitive cationic current attributable to transient receptor potential cation channel subfamily M member 5 (TRPM5); and CC-type 3, displaying mainly a noisy and voltage-dependent K+ current typical of potassium calcium-activated channel subfamily M alpha 1 (BKCa, KCNMA1). Pharmacological experiments, immunocytochemistry and rt-PCR confirmed the molecular expression of KCNA5, TRPM5 and KCNMA1. Mild extracellular acidification (pH = 6.2) rapidly and reversibly blocked TRPM5-like current, both inward and outward. Furthermore, 100 μM ATP induced metabotropic responses, evoking coupled intracellular Ca2+ release and activating TRPM5-mediated currents, as demonstrated by experiments with patch-clamp and FURA-2 calcium imaging. These findings reveal that human CCs integrate extracellular acidity and purinergic signals via distinct ion channels, suggesting a role as electrochemical sensors of the follicular microenvironment.