Figure 2. Effect of hyperosmolarity on chemoreceptor discharge activity.

A, single-fibre nerve activity following an increase in perfusate osmolarity from 297 to 330 mosmol l⁻¹, caused by the addition of NMDG to the saline (upper bar). Replacement of NMDG with Na⁺ resulted in an increase in perfusate [Na⁺] without further change in osmolarity (lower bar). B, single-fibre nerve activity (means ±s.e.m.) from 4 carotid bodies, before (Control) and following switching of the perfusate to hyperosmolar saline at constant [Na⁺] (+20 % osmolarity), and hyperosmolar saline at increased [Na⁺] (+20 % Na⁺). The increase in osmolarity significantly decreased frequency compared with control (* P < 0.001, n = 4), but frequency was not different from control following an isosmotic increase in [Na⁺]_o (P= 0.8).