Intracellular Ca2+ oscillations, initiated by the activation of IP3 receptors and orchestrated via intricate positive and negative feedback loops, can be subject to frequency modulation, an example of which is the increase in oscillation frequency with increasing stimulus strength. Caffeine is known to bind to and sensitize the ryanodine receptors, resulting in their opening in response to lower calcium ion concentrations. Do you think caffeine would tend to increase (I) or decrease (D) the frequency of calcium ion oscillations in stimulated cells? Write down I or D as your answer.