to control fig8 c this demonstrates na is the primary charge carrier through pbo 5 pbo 8 channels to determine the cation selectivity of the pbo 5 pbo 8 ion channel we substituted extracellular na with equivalent k in k ringer 39 s solution i v relationships were not significantly different p gt 0 05 two way anova compared to na ringers control fig8 d additionally strong inward rectification was present in i vs determined in k ringers demonstrating rectification was not due to ion selectivity taken together these data demonstrate pbo 5 pbo 8 encodes a non selective inwardly rectifying cation channel next ca 2 permeability of the pbo 5 pbo 8 ion channels was assayed the i v relationships under three ca 2 concentrations 1 mm control 3 mm and 10 mm were determined increasing calcium to 10 mm resulted in a positive shift in reversal potential from control fig9 a to better resolve calcium permeability nacl was replaced with nmdg in the extracellular solution making ca 2 the only relevant extracellular ion increasing ca 2 in this solution revealed that pbo 5 pbo 8 channels are calcium permeable increasing ca 2 10 fold caused a 50 mv shift in reversal potential compared to control fig9 b interestingly h evoked inward currents were significantly reduced as extracellular ca 2 was increased.