Cold shock induces a Ca²⁺-dependent K⁺ efflux. A, K⁺ efflux from P. tricornutum cells during a cold shock. A K⁺ microelectrode was placed adjacent to densely packed P. tricornutum cells to measure K+ in the immediate vicinity of the cell. A cold shock was applied by perfusion. The increase in extracellular K⁺ is the result of K⁺ efflux from the cells. The temperature in the dish is also shown (upper trace). B, Extracellular K⁺ during a cold shock in the absence of external Ca²⁺ (perfusion with ASW-Ca²⁺ + 200 μM EGTA). C, Mean change in extracellular K⁺ around P. tricornutum cells during a cold shock. “No cells” indicates control experiments where the experimental setup was identical, but no P. tricornutum cells were present in order to assess whether the performance of the K⁺ microelectrode was influenced by temperature. The total number of replicates for each treatment are shown in parentheses, error bars = se.