guanine(out) + Na(+)(out) = guanine(in) + Na(+)(in)
guanine(out) + na(+)(out) = guanine(in) + na(+)(in)
guanine(out) + Na(+)(out) = guanine(in) + Na(+)(in)
guanine(out) + na(+)(out) = guanine(in) + na(+)(in)