Ca(2+)(in) + Na(+)(out) => Ca(2+)(out) + Na(+)(in)
ca(2+)(in) + na(+)(out) => ca(2+)(out) + na(+)(in)
Ca(2+)(in) + Na(+)(out) => Ca(2+)(out) + Na(+)(in)
ca(2+)(in) + na(+)(out) => ca(2+)(out) + na(+)(in)